Compression-induced charge disproportionation in the orthorhombic NaTaO _3 (100) monolayer: Structural, electronic, and magnetic transitions

Perovskite transition-metal oxides as low-dimensional 2D materials have recently attracted special attention owing to their unique properties, which can be valuable to many applications. We have theoretically explored orthorhombic (100) NaTaO _3 monolayers through DFT calculations, aiming at deep insights of the one-layer limit impact on their physical properties. The monolayer is initially metallic and magnetic, in contrast to its semiconductor non-magnetic bulk. In-plane biaxial strain induces a charge disproportionation state in surface Ta atoms, taking the monolayer to an energy minimum through structural, electronic, and magnetic transitions. A monoclinic semiconductor non-magnetic monolayer is then obtained. Comparisons with multilayered films unveil that such a phenomenon is restricted to the monolayered system. Further hybrid calculations adjust its bandgap, revealing anisotropic absorption peaks in the visible light region. The predictions are of major importance when the two-dimensional limit is approached for polar perovskites, contributing to the applications of monolayered oxides in developing nanoelectronics. Graphical abstract Charge disproportionation on surface Ta atoms induced by compressive biaxial strain promotes structural (orthorhombic to monoclinic), electronic (metal to semiconductor), and magnetic (to non-magnetic) transitions in the (100) NaTaO 3 monolayer.